Real gas transport through nanopores of varying cross-section type and shape in shale gas reservoirs

A model for real gas transport in nanopores of shale gas reservoirs (SGRs) was proposed on the basis of the weighted superposition of slip flow and Knudsen diffusion, where the ratios of the intermolecular collisions and the molecule-nanopore wall collisions to the total collisions are the weighted factors of slip flow and Knudsen diffusion, respectively. The present model takes account of slip effect and real gas effect, additionally, the effects of cross-section type and its shape of nanopores on gas transport are also considered in this paper. The present model is successfully validated against existing molecular simulation data collected from different sources in literature. The results show: (1) the present model is reasonable to describe all of the gas transport mechanisms known, including continuum flow, slip flow and transition flow in nanopores of SGRs; (2) the cross-section type and shape of nanopores both affect gas transport capacity: at the same cross-sectional area, gas transport capacity of nanopores with a circular cross section is greater than that with a rectangular cross section, and gas transport capacity of nanopores with a rectangular cross section decreases with an increasing aspect ratio; compared to the cross-section type, the effect of the cross-section shape on gas transport capacity is stronger; (3) a real gas effect improves gas transport capacity, which becomes more obvious with an increasing pressure and a decreasing pore size; (4) and compared to nanopores with a circular cross section, the effect of real gas effect on gas transport capacity of nanopores with a rectangular cross section is stronger, and the effect increases with an increasing aspect ratio. The proposed model can provide some theoretical support in numerical simulation of reservoir behavior in SGRs.